1. Field of the Invention
The invention relates to an electric power steering system including an auxiliary power supply.
2. Description of the Related Art
One of the conventional electric power steering system includes an auxiliary power supply device connected in series with a main power supply. The electric power steering system makes a switchover between charging to a capacitor serving as an auxiliary power supply from the main power supply and discharging to a motor driving circuit from the main power supply and the capacitor, based on a charging and discharging threshold changed on the basis of an energy residual amount in the capacitor. Japanese Patent Application Publication No. 2009-166679 (JP 2009-166679 A) describes an example of the configuration of such a conventional electric power steering system.
The conventional electric power steering system is configured such that the capacitor discharges electric power to the motor driving circuit, and is not configured such that the capacitor discharges electric power to the main power supply. Thus, it is not possible to supply electric power to the main power supply from the capacitor.